package com.xbb.util;

public class MD5 {
	/*
	 *四个链接变量
	 */
	private final int A=0x67452301;
	private final int B=0xefcdab89;
	private final int C=0x98badcfe;
	private final int D=0x10325476;
	/*
	 *ABCD的临时变量
	 */
	private int Atemp,Btemp,Ctemp,Dtemp;

	/*
	 *常量ti
	 *公式:floor(abs(sin(i+1))×(2pow32)
	 */
	private final int K[]={
			0xd76aa478,0xe8c7b756,0x242070db,0xc1bdceee,
			0xf57c0faf,0x4787c62a,0xa8304613,0xfd469501,0x698098d8,
			0x8b44f7af,0xffff5bb1,0x895cd7be,0x6b901122,0xfd987193,
			0xa679438e,0x49b40821,0xf61e2562,0xc040b340,0x265e5a51,
			0xe9b6c7aa,0xd62f105d,0x02441453,0xd8a1e681,0xe7d3fbc8,
			0x21e1cde6,0xc33707d6,0xf4d50d87,0x455a14ed,0xa9e3e905,
			0xfcefa3f8,0x676f02d9,0x8d2a4c8a,0xfffa3942,0x8771f681,
			0x6d9d6122,0xfde5380c,0xa4beea44,0x4bdecfa9,0xf6bb4b60,
			0xbebfbc70,0x289b7ec6,0xeaa127fa,0xd4ef3085,0x04881d05,
			0xd9d4d039,0xe6db99e5,0x1fa27cf8,0xc4ac5665,0xf4292244,
			0x432aff97,0xab9423a7,0xfc93a039,0x655b59c3,0x8f0ccc92,
			0xffeff47d,0x85845dd1,0x6fa87e4f,0xfe2ce6e0,0xa3014314,
			0x4e0811a1,0xf7537e82,0xbd3af235,0x2ad7d2bb,0xeb86d391};
	/*
	 *向左位移数,计算方法未知
	 */
	private final int s[]={7,12,17,22,7,12,17,22,7,12,17,22,7,
			12,17,22,5,9,14,20,5,9,14,20,5,9,14,20,5,9,14,20,
			4,11,16,23,4,11,16,23,4,11,16,23,4,11,16,23,6,10,
			15,21,6,10,15,21,6,10,15,21,6,10,15,21};


	/*
	 *初始化函数
	 */
	private void init(){
		Atemp=A;
		Btemp=B;
		Ctemp=C;
		Dtemp=D;
	}
	/*
	 *移动一定位数
	 */
	private    int    shift(int a,int s){
		return(a<<s)|(a>>>(32-s));//右移的时候，高位一定要补零，而不是补充符号位
	}
	/*
	 *主循环
	 */
	private void MainLoop(int M[]){
		int F,g;
		int a=Atemp;
		int b=Btemp;
		int c=Ctemp;
		int d=Dtemp;
		for(int i = 0; i < 64; i ++){
			if(i<16){
				F=(b&c)|((~b)&d);
				g=i;
			}else if(i<32){
				F=(d&b)|((~d)&c);
				g=(5*i+1)%16;
			}else if(i<48){
				F=b^c^d;
				g=(3*i+5)%16;
			}else{
				F=c^(b|(~d));
				g=(7*i)%16;
			}
			int tmp=d;
			d=c;
			c=b;
			b=b+shift(a+F+K[i]+M[g],s[i]);
			a=tmp;
		}
		Atemp=a+Atemp;
		Btemp=b+Btemp;
		Ctemp=c+Ctemp;
		Dtemp=d+Dtemp;

	}
	/*
	 *填充函数
	 *处理后应满足bits≡448(mod512),字节就是bytes≡56（mode64)
	 *填充方式为先加一个0,其它位补零
	 *最后加上64位的原来长度
	 */
	private int[] add(String str){
		int num=((str.length()+8)/64)+1;//以512位，64个字节为一组
		int strByte[]=new int[num*16];//64/4=16，所以有16个整数
		for(int i=0;i<num*16;i++){//全部初始化0
			strByte[i]=0;
		}
		int    i;
		for(i=0;i<str.length();i++){
			strByte[i>>2]|=str.charAt(i)<<((i%4)*8);//一个整数存储四个字节，小端序
		}
		strByte[i>>2]|=0x80<<((i%4)*8);//尾部添加1
		/*
		 *添加原长度，长度指位的长度，所以要乘8，然后是小端序，所以放在倒数第二个,这里长度只用了32位
		 */
		strByte[num*16-2]=str.length()*8;
		return strByte;
	}
	/*
	 *调用函数
	 */
	public String getMD5(String source){
		init();
		int strByte[]=add(source);
		for(int i=0;i<strByte.length/16;i++){
			int num[]=new int[16];
			for(int j=0;j<16;j++){
				num[j]=strByte[i*16+j];
			}
			MainLoop(num);
		}
		return changeHex(Atemp)+changeHex(Btemp)+changeHex(Ctemp)+changeHex(Dtemp);

	}
	/*
	 *整数变成16进制字符串
	 */
	private String changeHex(int a){
		String str="";
		for(int i=0;i<4;i++){
			str+=String.format("%2s", Integer.toHexString(((a>>i*8)%(1<<8))&0xff)).replace(' ', '0');

		}
		return str;
	}
	/*
	 *单例
	 */
	private static MD5 instance;
	public static MD5 getInstance(){
		if(instance==null){
			instance=new MD5();
		}
		return instance;
	}

	private MD5(){};

	public static void main(String[] args){
		String str=MD5.getInstance().getMD5("");
		System.out.println(str);
	}
}
